1. Field of the Invention
The present invention relates to an electromagnetic interference (EMI) noise shielding device, and more particularly to an EMI noise shielding device capable of filtering a noise in a feedback voltage (Vfb).
2. Description of Related Art
In general, a conventional digital power supply control device outputs and supply an electric power with appropriate current and voltage values to an electric appliance in order to achieve the effects of protecting related circuits, improving the lifespan of the electric appliance, and saving electric power.
However, if a digital power width modulation (PWM) output unit of the conventional digital power supply control device receives a plurality of sample control signals outputted by a duty cycle modulation control unit, a power switching unit will modulate and output an appropriate steady-state voltage for the operation of an electric appliance according to the sample control signals. Before the sample control signals are outputted, signals containing noises are generally amplified by an amplification circuit. If the digital PWM output unit modulates a duty cycle of an analog pulse train outputted from the power switching unit, or there may be a modulation, the power switching unit may be interfered by the signals transmitted from the digital PWM output unit, so that a high signal among the signals may be mistaken as a low signal, or the low signal among the signals may be mistaken as a high signal. As a result, the precision of the modulated duty cycle of the analog pulse train outputted by the power switching unit is lowered, and the voltage outputted by the power switching unit may not be a steady-state voltage as required, and the electric appliance cannot operate normally.
Therefore, finding a way of filtering the noise signals in the sample control signals and avoiding possible misjudgments made by the power switching unit during the modulation process demands immediate attentions and feasible solutions.